**Appendix C. High-Pressure Region**

The pressure contours at the front and rear of the pod are shown in Figure A4 to describe the high-pressure region and the form of oblique shockwaves coexist with normal shockwaves. Figure A4 indicates that because the front wave propagation speed is much higher than the operating pod speed (150 m/s), a high-pressure region is created in places far from the nose. This is contrary to the phenomenon that occurs at a *vP* of 350 m/s, in which the high-pressure region occurs right in front of the nose. This means that when the local flow exceeds supersonic speed, the compression wave gets increasingly closer. This high-pressure region separates the pressure in front of the pod into two distinct regions: a disturbed region (orange-red color) and an undisturbed region (green color) that is at the initial tube pressure. A severe shock phenomenon occurs at a *vP* of 350 m/s, which did not appear at a *vP* of 150 m/s. The low-pressure region is not significant compared to other pressure regions behind the pod. Hence, it was not observed in the pressure contour.

**Figure A4.** Pressure contour of pressure waves generated at the front and rear of the pod. The largest red regime describes the high-pressure regime.
